This invention relates to a kneader for mixing or kneading powder materials for ceramics, powder metallurgy, chemical industry or the like and more particularly to a construction of seals for bearings of mixing blades for a kneader.
In hitherto used kneading apparatus as kneaders or the like, at least one mixing blade has been used for kneading powder materials supplied into a vessel. In order to prevent the powder material from escaping out of the apparatus, it has been required to provide a seal between the vessel and a shaft rotatively driving the mixing blade.
For this purpose, for example, a seal consisting of a gland packing 53 and/or an oil seal 54 is provided at a location where a vessel 50 contacts a shaft 52 for a mixing blade 51 to prevent a powder material from leaking through clearances 55 between the vessel 50 and the shaft 52 out of the kneader as shown in FIG. 1.
With such a sealing method, however, sealing materials of the gland packing 53 or the oil seal 54 tend to wear owing to sliding movements between the shaft 52 and the gland packing 53 or oil seal 54, so that part of the sealing materials are mixed with a powder material causing contamination. Moreover, part of the powder material flows through the clearances 55 into sealed portions, so that the powder material functions as abrasives to scrape or shave the shaft 52, resulting in metal components such as iron and the like of the shaft entering the vessel to contaminating the powder material.
Such components which may be mixed in the powder material are of a very small amount to an extent that it is unnoticeable by a normal chemical analysis. However, in the ceramic industry field, if the components, particularly the Fe component, is mixed in with the powder materials, there are often problems such as local change in color or tint of products of the powder material after sintering depending upon the kind of powder material. In general, powder materials of finer particles are apt to cause such a trouble of the local change in color. Therefore, it has been expected to develop a seal which does not cause such a contamination.